Re: [PATCH 3/5] iommu/vt-d: Do deferred attachment in iommu_need_mapping()

From: Lu Baolu
Date: Mon Feb 17 2020 - 21:38:23 EST

Hi Joerg,

Thanks for doing this.

On 2020/2/18 3:38, Joerg Roedel wrote:
From: Joerg Roedel <jroedel@xxxxxxx>

The attachment of deferred devices needs to happen before the check
whether the device is identity mapped or not. Otherwise the check will
return wrong results, cause warnings boot failures in kdump kernels, like

WARNING: CPU: 0 PID: 318 at ../drivers/iommu/intel-iommu.c:592 domain_get_iommu+0x61/0x70


Call Trace:
ahci_port_start+0xfb/0x1f0 [libahci]
ata_host_start.part.39+0x104/0x1e0 [libata]

With the earlier check the kdump boot succeeds and a crashdump is written.

Signed-off-by: Joerg Roedel <jroedel@xxxxxxx>
drivers/iommu/intel-iommu.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
index 42cdcce1602e..32f43695a22b 100644
--- a/drivers/iommu/intel-iommu.c
+++ b/drivers/iommu/intel-iommu.c
@@ -2541,9 +2541,6 @@ static void do_deferred_attach(struct device *dev)
static struct dmar_domain *deferred_attach_domain(struct device *dev)
- if (unlikely(attach_deferred(dev)))
- do_deferred_attach(dev);

This should also be moved to the call place of deferred_attach_domain()
in bounce_map_single().

bounce_map_single() assumes that devices always use DMA domain, so it
doesn't call iommu_need_mapping(). We could do_deferred_attach() there

Best regards,

return find_domain(dev);
@@ -3595,6 +3592,9 @@ static bool iommu_need_mapping(struct device *dev)
if (iommu_dummy(dev))
return false;
+ if (unlikely(attach_deferred(dev)))
+ do_deferred_attach(dev);
ret = identity_mapping(dev);
if (ret) {
u64 dma_mask = *dev->dma_mask;